The present invention relates to ink jet printers having printhead priming and cleaning means and, more particularly, to priming and cleaning devices for selective priming and cleaning of ink jet printhead nozzles without contact therewith.
Ink jet printers usually include one or more linear arrays of nozzles contained on a planar surface of a printhead. Droplets of ink are ejected from the nozzles and directed toward a recording medium (e.g., paper) to print images thereon. Droplet ejection can be effected by, for example, piezoelectric transducers or thermal transducers (e.g., resistive heating elements) as is well known in the art. The nozzles are formed, for example, by etching a plurality of channels in one surface of a first silicon wafer, which is then adhesively bonded to a surface of another silicon wafer having sets of selectively addressable heating elements thereon. Each channel contains a heater element. The bonded silicon wafers are then diced along a line perpendicular to and intersecting the channels to form a planar nozzle face of the printhead, which contains a linear array of nozzles (corresponding in number to the number of channels formed in the first wafer). See, for example, U.S. Pat. Nos. 4,878,992 to Campanelli; Re. 32,572 to Hawkins et al; and 4,774,530 to Hawkins, the disclosures of which are incorporated herein by reference. Pagewidth ink jet printheads may be fabricated by assembling fully functional printhead subunits on a structural bar in one of two basic ways; viz., staggered on opposite sides of the structural bar or abutted in an end-to-end fashion on one side of the structural bar. See, for example, U.S. Pat. Nos. 4,463,359 to Ayata et al. and 4,829,324 to Drake et al., respectively, for staggered opposite side and abutted end-to-end pagewidth printheads.
In order to eject droplets having a consistent size and ejection direction, the nozzle face of the printhead which contains the nozzles must be maintained free of any contamination, scuffs, or scratches. Any scratches or contamination on the nozzle face of the printhead, especially in the vicinity of a nozzle, can interfere with the formation of an ink meniscus at that nozzle, causing drop misdirection. Additionally, the nozzle containing surface or face of the printhead is frequently treated with a coating which is non-wettable by the ink. The non-wettable coating prevents ink from adhering to the planar, nozzle-containing surface of the printhead, which adhered ink can also interfere with the ejection of new droplets from the nozzles. Contact cleaning of nozzle-containing surfaces having such non-wettable coatings tends to frictionally wear the coating off, so that non-contact cleaning is preferred.
The processes which make these printheads result in nozzles having sharp edges. These sharp edges assist in the meniscus formation process, but also increase the probability of contamination in the nozzles, if cleaned by wiper blades, because these sharp edges tend to shear small pieces from wiping blades which then collect in the nozzles.
Air can occasionally be collected or ingested into the channels of the printhead which supply ink to the nozzles during operation of the printhead, disrupting the operation of those nozzles. This disruption is typically removed by priming. Priming can also be used to remove dirt or dried ink from the printhead nozzles. One source of dirt is because of the close proximity of the printhead nozzle face to the paper, which releases dust and particles, as well as due to the presence of airborne dust and other particles. Additionally, as discussed above, when wiping blades are used to wipe contaminants and residual ink from the planar nozzle face of the printhead, the sharp edges of the nozzles tend to wear or slice small pieces from the wiping blades, which further clog the nozzles.
A number of procedures are known for priming printheads with fresh ink. Pressure can be applied to the ink supply to force ink out through the nozzles. Alternatively, suction can be applied to all of the nozzles in the printhead to draw ink simultaneously through all the channels. As another alternative, suction can be applied to a lesser number of nozzles (i.e., not all of the nozzles) at a time through one or more tubes or small diameter hoses.
Copending U.S. application Ser. No. 07/777,043, filed Oct. 16, 1992, entitled "Movable Ink Jet Priming Station" to Fisher et al. and commonly assigned to the assignee of the present invention, discloses that positioning a small diameter tube closely adjacent, yet spaced away from, a nozzle-containing front face of the printhead removes more dirt by drawing in air located adjacent to the front face, as well as ink located in the channels. Accordingly, as compared to a single small diameter tube, a cleaning device which applies vacuum to all nozzles at the same time does not apply a force which is sufficient to adequately remove dirt from the nozzles. Additionally, much of the vacuum is lost through the large sealing surface of priming members which suction all nozzles at once. Furthermore, priming stations which suction all nozzles at once tend to leave ink on the front face of the printheads, which ink must be removed, for example, by wiping blades. As discussed above, minute pieces of blade material are cut from the wiping blades by the nozzles, contributing to recontamination of the nozzles.
U.S. Pat. No. 4,947,191 to Nozawa et al discloses an ink jet recording apparatus having an ink jet head provided with plural discharge openings and a partial capping member for covering a part of the plural discharge openings and applying suction only to the covered part of the plural discharge openings. The partial capping member is provided on a belt which is moved across the nozzles of the printhead to selectively locate the partial capping member adjacent to a small number of nozzles. The capping member of Nozawa et al contacts the printhead face along the array of nozzles and is moved along the array of nozzles. The capping member of Nozawa et al could scratch the printhead nozzle face, as well as wear away any coating material thereon. The present invention differs from Nozawa et al. at least in that the present invention provides a priming station which does not contact the areas of the printhead containing the nozzles and yet controls the spacing or gap between the priming and cleaning orifice and a pagewidth printhead over the entire length thereof.
U.S. Pat. No. 5,055,856 to Tomii et al. discloses an ink capping device for an ink jet printer which includes a cap for sealing the ink outlet portion of an ink jet printhead, a suction device for maintaining a proper ink level within the printhead, and a valve to regulate pressure within the printhead. The cap can be supported by and urged towards the printhead by a support member to compensate for displacement of the printhead with respect to the support member and maintain uniform pressure distribution at a contact surface between the cap and the printhead. By applying successive suction operations to the cap, in which the second suction operation is shorter than the first, the ink meniscus level is maintained at a proper level for printing despite extended exposure of the printhead to high temperatures. Tomii et al. does not disclose noncontact method of priming with controlled spacing between a suction nozzle and the nozzle face of a pagewidth printhead along the entire length of the printhead.
U.S. Pat. No. 4,878,992 to Campanelli discloses an ink jet printhead fabrication process wherein a plurality of printheads are produced from two mated substrates by two dicing operations. One dicing operation produces the nozzle face for each of a plurality of printheads and optionally produces the nozzles. A second dicing operation with a standard dicing blade severs the mated substrates into separate printheads. The dicing operation which produces the nozzle face is preferably conducted in a two-step operation. A first cut makes the nozzle face, but does not sever the two mated substrates- A second dicing cut severs the two substrates, but does so in a manner that prevents contact by the dicing blade with the nozzle face. Campanelli discloses a printhead having a ledge, but does not indicate a use for the ledge. The present invention uses such a ledge to control the spacing of a priming station therefrom.
U.S. Pat. Nos. 5,057,853 and 5,068,006, both to Fisher, disclose thermal ink jet printheads and method of batch production thereof. These patents disclose printheads with a stepped nozzle face, but have a photopatterned thick film layer sandwiched between the channel wafer and heater wafers, so that dicing operations to separate the aligned and bonded wafers into separate printheads do not require dicing of the thick film layer in the vicinity of the nozzles, thereby preventing formation of burrs which affect droplet directionality. These patents include embodiments with ledges on the nozzle face, but do not recognize, teach, or disclose a use for the ledges. To the contrary, the ledges of Fisher are impediments to blade cleaning of carriage type, reciprocable printheads, unless removed to provide planar access to the nozzle containing faces.